In the mass production of bubble or blister packs, it is standard to form a base sheet or foil with an array of pockets or blisters, then to advance this foil with the pockets open upward so they can be filled with the product to be packaged. Then a cover foil is applied to the upwardly directed upper face of the filled base foil and is adhered to it in the webs between adjacent pockets. The cover foil can be made to adhere by heating it or a face of it so that a good bond is formed and the product is hermetically encased in the now closed products. Then the laminated-together foils are cut apart in the webs between the pockets to form individual packages.
U.S. Pat. No. 5,608,277 of Scheifele describes a system where the cover foil is heated by passing it between a pair of heater plates. During normal operation the heater plates are closely juxtaposed with the cover foil which is oriented in a vertical plane. If the system is shut down temporarily or not in use, the two heater plates are shifted back away from the cover foil so that they do not overheat and, possibly, burn it. Such heater plates work well during the production run, but getting them up to the desired temperature and accurately controlling their temperatures is a problem, so that at the start of the run a certain amount of the cover foil is inadequately heated and does not adhere to the base foil, creating unusable packages, and during the run it is not possible to precisely adjust the temperature of the cover foil.
In German 198 50 143 of Bar a near infrared (NIR) emitter, e.g. with a wavelength of 1.4 μm, is used to heat the cover foil. Such a heater has two emitter tubes each having a tungsten filament that is heated electrically. The power supplied to the filaments is regulated to control the temperature to which the cover foil is heated, this temperature being of course also dependent on the spacing of the foil from the heater, the composition of the foil, and the speed at which the foil moves past the heater.
The problem with this system is that the cover foil is typically fairly fragile and also flammable. If the foil stops, it can quickly be melted through or set afire, and the same thing can happen simply if the foil conveyor jams or the foil breaks. The existing systems therefore present a fire hazard and also often require that the surroundings be somehow protected from the occasional accident.